THE CELL. 29 



tion of* the nuclear membrane a closer relation exists between 

 the nuclear and protoplasmic structures. The most essential 

 part of karyokinesis is the division of the chromatin of the 

 ; mother cell into two quite equal parts for the daughter cells. 



The chromatin divides itself into two equal parts, the 

 so-called chromosomes. They may be loop-shaped, rod-shaped, 

 or granular. Their numbers may be two, four, eight, sixteen, 

 up to one hundred. The shape, as well as the number, of 

 chromosomes is different, and is characteristic for cells of 

 different animal species. 



An exactly equal division of the chromatin takes place by a, 

 longitudinal splitting of the chromosomes. 



In the protoplasm at the same time very important changes 

 take place, namely, the division of the centrosome, and the 

 arrangement of the protoplasm in radially disposed lines around 

 the centrosome. The two parts of the centrosome move to the 

 poles of the cell, and between them is formed the central spindle 

 in the protoplasm. This is shown in Figs. 7 and 8. 



The whole process of mitosis may be divided into five 



stages : 



1. Prophase; 



2. Mother star stage ; 



3. Metaphase metakinesis ; 



4. Anaphase ; 

 o. Telophase. 



The prophase consists in the preparation of the resting 

 nucleus for division. Inside the nucleus, the nuclear frame- 

 work arranges itself in threads which are covered in the 

 beginning with thickenings. These threads of different lengths 

 become smooth on their surfaces and twisted, so that there is 

 formed a coiled mass (Knauel) (Figs. 4, a, 4, b, 5, 6). 



The originally rather thick coil or knot of chromatin threads 

 becomes looser, and the chromosomes assume their characteristic 

 forms of loops, rods, etc. (Fig. 4, c, Fig. 7). 



The nucleolus always vanishes during the formation of the 

 coil. The centrosome divides at the beginning of these changes 

 into two parts, which are joined from the first by fine fibrils in 



